1. Field of the Invention
This invention relates to a drive pulley system for an internal combustion engine. More particularly, the present invention relates to an improved pulley system which produces enhanced traction between the pulley and a drive belt in wet operating conditions.
2. Disclosure Information
Pulley drive systems for powering the accessories of internal combustion engines are used to transmit power through a belt, with the belt making frictional contact with the face of the pulleys. The use of pulley systems to accomplish the transfer of power has been proven to have certain deficiencies inasmuch as pulleys rely upon friction for their motive force. Once the friction is lost between the pulley and the belt, as may be the case with an accumulation of water on the surface of the pulley system, slip occurs. Water on the surface of the pulley system causes the coefficient of friction between the belt and the pulley faces to decrease, causing either an objectionable squealing noise which will be audible to the driver as the belt slips or a change in speed of the driven accessory.
Currently, conventional multi-ribbed belts and pulleys are used on several drive systems with automobile engines. The pulley's circumferential grooves for receiving friction belts such as multi-rib belts have grooved surfaces which are very smooth; therefore, the coefficient of friction between the surfaces of the grooves relative to the friction belt is very low. Prior work has focused on improving friction within different belt systems or has focused on modifying the belt itself. Due to the different flexural properties of the belts, a solution that corrects for the loss of friction with one belt system cannot be readily applied to solving the same problem with another belt system.
U.S. Pat. No. 1,601,662 describes transferring power to a laterally flexible belt with a steel laminate, used with either a variable effective diameter or a fixed diameter pulley. This belt is very different from a multi-ribbed belt, which is laterally fixed and rigid. Also the tensions associated with a variable speed gear are higher than those associated with a constant speed gear.
U.S. Pat. No. 4,781,660 describes transferring power to a chain belt operating at high speed at a small wrap angle. A V-pulley described in the U.S. Pat. No. 4,781,660 comprises a pair of conical pulley faces that the chain belt contacts, with each being provided with a rough surface. The smaller wrap angle taught would also lower the total torque capacity between a belt and the pulley. In addition, the frequency of the roughness defined and shown in this is too high to be effective with a multi-ribbed belt, because the multi-ribbed belt would lift out of the fixed multi-ribbed belt pulley.
U.S. Pat. No. 4,898,567 describes a V-block belt system aimed at reducing noise levels during operation. The system relies on the assistance of a special belt with intermittently spaced V blocks. The type of belt taught differs significantly from a smooth multi-ribbed belt.
U.S. Pat. No. 4,905,361 describes a conventional multi-ribbed pulley, designed to work with a multi-ribbed belt. The invention teaches the addition of axial grooves which extend in an axial direction over a surface of the pulley in which the circumferential groove is formed, and a higher friction surface which is formed by roughening the surface. However, with this invention, combined with the characteristic hardness of the rib stock rubber of at least 65 shore durometer of all known K section V-ribbed belts, the belt would simply be elevated out of the grooves and would ride across the top of the bumps with less effective wrap surface. Hence, there would be lower friction and subsequently lower belt/pulley torque capacity than a pulley without the roughness as described in this patent.
It is known that modified multi-ribbed belts having smaller V angles perform slightly better under wet-slip conditions than conventional multi-ribbed belts. This could be because the tips of the pulley dig into the belt rib valleys and create a local pressure wedging in this area. The sharper, longer V of the belt provides full rubber to steel contact during the wet slip situation, which prevents hydroplaning as the belt digs into the bottom of the pulley. However, this technique causes undue wear to the belts because the tip loads will wear out the rib section of the belt, eliminating future point contacts.
The current invention applies the concept of creating localized high pressure areas through the pulley's geometric characteristics. The system modifies the amount of space between adjacent conical faces of the pulley, thereby creating high pressure areas between the pulley and the belt at the belt/pulley interface.
Clearly, it is desirable to be able to have an improved multi-ribbed belt pulley system that will compensate for wet conditions and prevent the belt from slipping on the pulley, thereby preventing a squealing sound as the belt loses traction.